There are many methods known in the computer art which can archive and retrieve textual expressions (words and phrases) in natural language. Primarily, these methods use key words as indexes to archive and retrieve these textual expressions. However, many things, particularly things in the area of multimedia (images and sounds), are not easily described using key words indexes. Often multimedia information like the sound of a dog barking, images shown in certain pictures, or the steps performed in a dance require more descriptive indexes than the prior art key words can provide. Key word indexes have failed to be descriptive enough because they can not easily identify the difference between a thing and an action, describe what agent performs a given action, or describe what object is acted upon. These key word failures, and others, create ambiguities when key words are used to identify and catalog information.
The key word indexes of the prior art lack the grammatical structure needed to make them more descriptive. Key word phrases have no structure because the words in the phrases lack two things: 1. a function and 2. a relationship. In a natural language, (i.e., languages spoken by humans) function and relationships of the words are provided by the language grammar (grammar rules). For example, in the English natural language phrase "a man will fall into the pool", each word has a function and a relationship to the other words in the phrase dictated by English grammar. Functionally, "man" and "pool" are nouns and "fall" is a verb. Relationships exist because, syntactically, "man" is the subject of the sentence, and, semantically, it is the theme of an action; "fall" is the predicate which describes the action; and "pool", according to the English syntax, the locational object of the sentence, describes the location of the action. Often, the object of a sentence is the recipient of the action of an agent; and the subject of the sentence is the agent of an action; for instance, "the woman pushed the ball". The word "agent" is used to describe the typical subject; that is, by default subjects are assumed to be agents. The explicit distinction between agent-subject and theme-subject is not made, since it does not affect the logic of the proposal. Similarly, we will use the word "object" to cover several syntactic functions, such as direct object, object of a preposition, and indirect object. Notice that this slot can have multiple fillers when there is more than one object as in "The child dropped the ball into the pool", where "the ball" is the direct object and "into the pool" the locational object of the action. (In all our examples we will use only single fillers). Natural languages use different kinds of grammatical rules to affect the meaning of the words. These include: defining parts of speech, ordering words in the phrase, and using word prefixes or endings, etc. Since key words, even in phrases, lack these grammatical rules, they can be less descriptive and ambiguous. For example, when the phrase "man will fall into the pool" is parsed into words, the key word "fall" has no function (it could be a verb or a noun) and could be ambiguously interpreted as "drop" or a "season of the year". Furthermore, splitting the key word phrase "cat eats mouse" into "cat", "eats", and "mouse", yields a sequence of key words with no relationship. Because there is no way to tell which word is the subject and which is the object, the interpretation becomes ambiguous. The phrase could mean: "cat eats mouse", "mouse eats cat", or "cat and mouse eats".
The problem is compounded when synonyms, hypernyms (words of a broader genus which include the key word) or hyponyms (words within the key word genus) of key words are used to expand a key word search to retrieve data. This is frequently required in Information Retrieval systems because often users use slightly different words that are not found via a direct match. For example, a synonym (hypernym) of "fall" like autumn (season) would give erroneous results when searching a database for a match to the key word "fall" which really meant "drop".